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Humpback chub populations in the Little Colorado River and the Black Rocks area on the upper Colorado River appear relatively stable in number of fish, but declines have been apparent in other locations (USFWS 1990b). COLORADO RIVER FLOODPLAIN North temperate riverine, or lotic, ecosystems are dynamic and complex. Large river systems are composed not only of the mainstream channels in which water is maintained most or all of the year, but an integral, natural part of these rivers are upland habitats that are inundated during the higher water levels that are usually associated with spring flows. These seasonally flooded habitats are major contributors to the biological productivity of the river system by providing inputs of nutrients and making terrestrial food sources available to aquatic organisms (Hesse and Sheets 1993) . The extent of flooded wetlands in the Colorado River has been reduced by the construction and operation of water resources development projects (Carlson and Muth 1989), and the remaining flooded uplands have great importance for recovery of endangered fishes. Studies of the major floodplain rivers of the world have documented the high value of flooded bottomlands and other flooded uplands for fish production (e.g., Welcomme 1979). Because fishes are highly mobile, many species are able to take advantage of food sources made available by flooded lands. Indeed, many fishes have developed migratory strategies that allow them to utilize inundated areas as spawning, nursery, and foraging areas (Lowe- McConnell 1975; Welcomme 1979). In this context, a rich food source of terrestrial origin may enhance fish growth, fecundity, and/or survival. Use of these inundated floodplains increases the energy available for spawning and is necessary for reproductive success in some species (Finger and Stewart 1987). In many cyprinid fishes, spawning is associated with seasonal rains and flooding of rivers, and it has been found that flood-related changes in the river environment not only induce spawning for many species, but these changes comprise the ultimate factors limiting the survival of eggs, larvae, or young fish (Hontela and Stacey 1990). Loss of inundated floodplain habitats in the Missouri River Basin has been associated with a concomitant reduction of as much as 98 percent of fish biomass (Karr and Schlosser 1978). Inundation of floodplain during spring flows also provides areas with warmer water temperatures, low velocity resting habitat, and cover from predation in flooded terrestrial vegetation. Recent studies in the Colorado River system have shown that the life histories and welfare of native riverine fishes is linked with the maintenance of a natural or historic flow regimen; i.e., a hydrological pattern of high spring and low autumn-winter flows that vary in magnitude and duration depending on annual precipitation patterns and runoff from snowmelt (Tyus and Karp 1989, 1990). This relationship is so evident to ichthyogists that it has been predicted that stream regulation that results in loss of flooding will result in extirpation of many native fish species in the Colorado River system (Minckley and Meffe 1987). 7